1. Field of the Invention
The present invention relates to an imaging lens unit equipped with a photographic optical system and an image pick-up device, a camera body on which the imaging lens unit is mounted removably, a camera system consisting of the imaging lens unit and camera body, and an interchangeable lens camera which makes many electrical connections for information transmission and operation control between the lens unit and camera body.
2. Description of the Related Art
Conventionally, removable-lens camera systems in which an image taking lens is mounted removably on a camera body is known in the field of film cameras.
Recently, digital cameras with removable lens units have been proposed in the field of digital cameras as in the field of film cameras.
For example, a camera system with a removable lens unit has been proposed in which multiple projections are formed on the outer periphery of the base end of a lens unit which unites an image taking lens and image pickup device, engaging parts to be engaged with the projections are formed in a lens mount on the camera body, the lens unit is turned by engaging the projections on the lens unit with the engaging parts on the lens mount, and thereby a connector in the lens unit is connected with a connector on the camera body (see, for example, Japanese Patent Laid-Open No. 2003-156790).
With this technique, electrical contacts of the connector on the camera body are exposed when the lens unit is not mounted on the camera body. Consequently, if an electrostatically-charged hand is brought near the electrical contacts, electrostatic discharge may cause trouble such as breakdown of internal elements or malfunctions of the camera system. Also, if the lens unit is connected to the camera body when it is electrostatically-charged, the electrostatically-charged lens unit will discharge into the camera body. This may result in breakdown of internal elements or malfunctions of the camera system.
A camera has been disclosed, which is equipped with a lens mount section in which a removable image taking lens is mounted, and an image pickup means which picks up an image of a subject formed by the image taking lens, wherein the camera is further equipped with a lens detection means which detects whether an image taking lens is mounted in the lens mount section, in order to prevent the camera from malfunctioning if static electricity is applied to the camera by a human body or the like with an image taking lens yet to be mounted; and power shutdown means which shuts down power supply to the image pickup means if the lens detection means detects that no image taking lens is mounted (see, for example, Japanese Patent Laid-Open No. 9-5850).
This technique has a problem in that it tends to increase costs because the camera must be equipped with a lens detection means which detects the presence or absence of an image taking lens and a power shutdown means which shuts down power supply to the image pickup means when no image taking lens is mounted.
This camera can prevent malfunctions because it shuts down power supply as appropriate. However, since the electrical contacts of the camera body is electrically connected with internal circuits, even if power supply is shut down, there remains a danger that electrostatic discharge may cause breakdown of internal circuits if an electrostatically-charged human body or the like is brought near the electrical contacts.
With interchangeable lens cameras, when the lens unit and camera body are coupled, electrical coupling must be provided simultaneously for both communications and power supply between the lens unit and camera body. For that purpose, connection terminals are provided in the mount section. Since the connection terminals are exposed, for example, on the camera body when no lens unit is mounted on the camera body, if they are touched accidentally with a metal strip such as a coin or a clip, they may cause an electrical short circuit, damaging internal circuits. To solve this problem, various techniques have been developed.
For example, there is a technique which involves arranging multiple camera-body-side electrical connection terminals approximately around an optical axis, installing at least two power supply terminals in such a way as to provide height differences with steps formed in the direction of contact, forming juts which protrude from the connection terminals in the direction of contact at locations orthogonal to the connection terminals, and forming missing parts at locations which correspond to the juts when mounts are coupled and decoupled (see, for example, Japanese Patent Laid-Open No. 7-34094).
This technique provides steps at placement locations of the power supply terminals in the camera mount section to prevent any metallic foreign object getting inside from causing a short circuit. Since this technique provides height differences among terminals, it cannot deal with shapes other than flat shapes. Also, since the technique handles only power supply terminals, problems of noise, interference with other terminals, etc. remain to be solved.
An interchangeable lens has been proposed which has urging members for urging contactors so that contactors in the interchangeable-lens mount section will come into contact with contactors on the camera body, wherein the contactors are arranged on the same circumference in a plane perpendicular to the optical axis of the lens in such a way that multiple contactors slide when the lens is turned, and power supply terminals are spaced differently from other terminals (see, for example, Japanese Patent Laid-Open No. 4-11850).
This technique prevents electrical short circuits by placing terminals at different intervals so that power supply terminals or ground terminals will not touch signal lines when the lens is mounted and removed. However, it cannot deal with trouble caused by insertion of a foreign object.
Conventional single-lens reflex cameras almost do not need communications functions between lens and body. Thus, they have a small number of terminals and it is difficult to accommodate multi-conductor cables. Also, terminals are placed in blocks, making it difficult to avoid noise depending on the type of electrical signal. Besides, there may be a problem of interference.
With interchangeable lens cameras, when no lens unit is mounted, it is necessary to keep dirt, dust, and other foreign matter from entering an opening provided in the mating part between camera body and lens unit. In the case of a lens unit with a built-in image pick up device, in particular, dirt or the like sticking to the connection terminals located between camera body and lens unit will reduce the accuracy of the camera greatly. Thus, such lens units must be kept free of dirt and the like.
To deal with this situation, an image pickup apparatus has been proposed which has a casing with an opening that allows light to enter an imaging lens unit; and a cover that can move between closing position and opening position of the opening, wherein the cover moves from the closing position to the opening position by being pushed when the imaging lens unit is mounted (see, for example, Japanese Patent Laid-Open No. 2003-099952).
This technique places a barrier in the camera mount section to prevent dirt and the like from entering a contact section and is applicable only when the direction of engagement between lens unit and camera body coincides with the direction of insertion. It is difficult to apply this technique to a mechanism which involves inserting the lens unit in the camera body and turning it around the optical axis to engage the lens unit with the camera body.
Besides, as a technique for keeping off dirt from surfaces of an image pickup apparatus when the lens unit is removed, an apparatus has been proposed which is equipped with a transparent cover to keep inner space of a structure airtight when the lens unit is removed (see, for example, Japanese Patent Laid-Open No. 2000-241869).
This technique can provide protection for optical parts because the camera mount section is equipped with the transparent cover. However, no mention is made of any electrical contact section. Protection for the contact section should be provided separately.